Since the first manufacture of direct current motors and generators, there has existed the problem of detection of worn brushes before they are worn to a point where they may damage a commutator or slip ring. Normally, the brushes, which are made of carbon, are not visible while in use, and their wear rates are not completely predictable. Thus, not infrequently, a brush will wear out before anticipated. When this occurs, it is possible that a metal cable connection to the brush, and which extends into the brush, will engage a commutator or slip ring (in case of A.C. device) and damage it. As an old problem, others have suggested solutions, and the patent art reveals a number of proposals. One of the latest is set forth in U.S. Pat. No. 4,024,525. As particularly illustrated in FIG. 4 of this patent, an elongated groove is cut in the brush, and a probe is positioned so that when the brush is worn to a selected point, the brush engages the probe and sets off an alarm. This requires auxiliary hardware to be included in the apparatus design, and in some instances, there is simply no room for it. In any event, it adds to the complexity and cost of the apparatus. A review of other patented indicators fails to reveal a simple but effective one.
It is the purpose and function of this invention to provide a simpler but effective worn brush indicator, being one that does not require any brackets or probes to be built into the using apparatus and one that can be operated without an auxiliary power source.